A vacuum processing apparatus for processing a substrate, which is a sample to be processed such as a semiconductor wafer, placed in a vacuum container having an inside capable of being evacuated to high vacuum with plasma generated using a processing gas fed into the vacuum container which has been evacuated to vacuum, and an electric field or magnetic field has been utilized for highly fine processing of a semiconductor device and the like.
A typical example of such processing is etching of thin films constituting a plurality of layers formed on the surface of a substrate by lithography. By this etching, a portion of the thin film which has remained uncovered with a mask such as photoresist formed over the upper surface of this thin film is removed (etched) using highly reactive particles or ions formed in plasma.
Since there is a demand for semiconductor elements obtained by such processing to have higher precision and higher density, more minute and higher precision processing is requested. As a result, processing into a shape with smaller width, especially etching into a trench with a smaller width is required. A technology to increase a so-called aspect ratio of a trench, that is, a ratio of the depth of the trench relative to its width which is an indicator of the characteristic of the cross-sectional shape of the trench becomes necessary.
In order to actualize a high aspect ratio of a trench with high precision when minute processing is carried out, it becomes necessary to differentiate the processing property or processing rate depending on the processing direction, in other words, to heighten anisotropy of the processing or to employ an appropriate selectivity, which is a ratio of the processing property between a member to be processed and another member.
With a view to satisfying such a request, a technology to process a surface of a shape, such as trench, to be processed in a specific direction (bottom surface, lower surface) while covering its side surface with a substance other than that to be processed has been developed. As such a substance covering a side wall therewith, a hydrocarbon-containing resin formed by polymerization in plasma in a vacuum container or a product in plasma such as carbon fluoride is used. By depositing these substances to the surface of a film to be processed, thereby covering the surface therewith and, at the same time, by applying bias voltage to a substrate to introduce ions in plasma to the surface of the substrate in a substantially vertical direction, processing is caused to advance into the bottom direction of a trench while protecting the side wall of the trench from particles of a reactive substance.
On the other hand, the formation of a protecting film on the side wall owes mainly to the deposition of a reaction product so that its formation greatly depends on the distribution of the reaction product. The distribution of the reaction product in a processing chamber inside of a vacuum container is not always uniform so that without any device, the formation of the protecting film on the side wall becomes uneven in the in-plane direction of the substrate, which may damage the uniformity of the processed shape remarkably.
The deposition of such a reaction product on the substrate surface is influenced largely by the temperature on the substrate surface. A technology to appropriately adjust the temperature of the substrate in the plane direction and provide suitable distribution of the protecting film on the side wall, thereby making the processed shape more uniform is known.
As such a conventional art, those disclosed in Japanese Patent Laid-Open Nos. H7 (1995)-249586 and H11 (1999)-97516 are known.
In the former document, disclosed is a processing apparatus for adjusting the temperature of a wafer by feeding a heat conducting He gas between a semiconductor wafer which is to be processed and the surface of a lower electrode on which the wafer is to be mounted, adjusting the pressure of the He gas, and adjusting the calorie transferred to the surface of the lower electrode from the wafer. Particularly, disclosed in this document is a processing apparatus equipped with a supply and exhaust unit and a pressure control mechanism for feeding a heat conducting gas to the outer circumferential side and center side of the lower electrode respectively in order to adjust the temperature of the wafer to be uniform without causing cooling unevenness.
In the latter document, on the other hand, disclosed is an apparatus equipped with a heat conducting He gas feed pipe, a bypass pipe for communicating the above-described pipe and a processing chamber existing at the outer circumference of a lower electrode on which a wafer is retained by electrostatic adsorption, and an open valve placed over this bypass pipe, which apparatus, when a power supply is blocked by some accident to preclude adsorption of the wafer, can retain the wafer on the electrode, because the valve is opened to cause a heat conducting gas to escape into a processing chamber.
The above-described conventional arts lack considerations on the below-described points and therefore cause some inconveniences.
When films constituting a plurality of layers are processed and first processing is switched to second processing during two films are in the desired form, a rapid change in temperature is necessary when different temperature conditions are employed before and after the processing. It takes much time to change the temperature in the conventional art. During this change, it is therefore necessary to terminate the processing or retard the processing rate. This causes a reduction in the processing efficiency. Alternatively, owing to excessive processing during a temperature change, the processed shape may be far different from the desired one.
In particular, on the interface between two different film layers, switch-over in a shorter time is required when the underlying layer is exposed. If not so, the underlying film is etched too much or the processed shape becomes an undesired one because processing is not conducted under predetermined conditions until variations in the conditions stop and switch-over is completed.
If the etching of the underlying film is suppressed by a reduction in the processing rate during the exposure of the underlying film or in advance thereof in order to avoid the above-described problem, time necessary for the whole processing increases, which may lead to a reduction in the processing efficiency or throughput.
When the processing conditions are different or materials for respective film layers are different, changes in processing characteristics such as selectivity in a short time are required. The above-described conventional arts do not however include consideration on the technology to actualize such processing.